<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>J_计算函数Calc</title>
    <style>
        .out-box{
            border:1px solid #ccc;
            width: 200px;
            height: 200px;
        }
        .demo{
            border:1px solid #ccc;
            height:100px;
            width: calc(100% - 20px) ;
        }

        .out-box{
            border:1px solid #ccc;
            width: 200px;
            height: 200px;
        }
        .demo{
            border:1px solid #ccc;
            height: calc(100% /3);
            width: calc(100% /3);
        }
    </style>
</head>
<body>
<div class="out-box">
    <div class="demo">
        慕课网：计算函数学习
    </div>
</div>
</body>
</html>